1. Field of the Invention
The present invention relates to a tilt servo control device and a tilt servo control method for compensating the tilt angle of a recording surface of an optical recording medium as defined by the angle between the normal to the recording surface of the recording medium and the optical axis of a light beam irradiating the recording surface.
2. Description of the Related Background Art
In order to correctly read information recorded on an optical disk such as a DVD (Digital Versatile Disk), it is necessary to irradiate a reading light beam perpendicularly relative to a recording surface of the optical disk. If the optical disk has a warp, or errors in the mechanical system are large, it is impossible to irradiate the reading light beam perpendicular to the recording surface of the optical disk, thereby deteriorating reading accuracy for the recorded information.
In view of this problem, information reproducing apparatus for reproducing information recorded on an optical disk are normally provided with a tilt servo control device for detecting the tilt between a pickup as information reading means of the apparatus and the optical disk and compensate the tilt by adjusting the direction of the pickup in accordance with the detected tilt or by providing a signal read out by the pickup with a tilt correcting process corresponding to the detected tilt, so as to suppress the deterioration in the information reading accuracy.
Further, in order to compensate the tilt, a tilt servo control device provided with a liquid crystal panel inserted into the optical axis is known (For example, Japanese Patent Laid-Open Publication No. Hei. 11-3531). In the case of the device, the liquid crystal panel is divided into a plurality of regions, and a phase difference is provided to a light beam passing through each of the regions of the liquid crystal panel so as to maximize the level of a signal (RF signal) read out from a recording medium by a pickup.
In optical disks, not only read only optical disks such as a CD-ROM and a DVD-ROM but also writable type optical disks such as a DVD-R, a DVD-RW and a DVD-RAM are included. It is desired that a single optical recording/playing apparatus can correspond to optical disks of any types for the purpose of recording and/or reproducing information. Therefore, it is necessary to mount a tilt servo control device that can properly perform tilt servo control for optical recording media of various different types in the optical recording/playing apparatus.